1. Field of the Invention
This invention relates to a method and an apparatus for processing images. More specifically, this invention relates to a method and an apparatus for adjusting an image on the basis of the characteristics of a display system.
2. Description of the Prior Art
Generally, the brightness and the color coordinates of the three colors, red, green, and blue, in a display system are characteristics of the display system itself; thus, those characteristics may not be exactly the same as those specified in some video specifications, for example, NTSC, EBU, etc. Therefore, an image usually has to be properly adjusted before being displayed on a display system such that the color and the brightness of the image will be displayed correctly.
As known to the people skilled in this art, the color coordinates of the three colors in a display system are different from those in some video specifications. The colors specified in the specifications can be generated by properly combining the colors of the display system on the basis of the laws of color matching. According to the laws of color matching, the relationship between colors and brightness in the display system (hereinafter as Red, Green, and Blue) and the specification (hereinafter as RedSPEC, GreenSPEC, BlueSPEC) can be represented as:RedSPEC=k1[a11Red+a12Green+a13Blue]  (Equation 1)GreenSPEC=k2[a21Red+a22Green+a23Blue]  (Equation 2)BlueSPEC=k3[a31Red+a32Green+a33Blue]  (Equation 3)
a11, a12, a13, a21, a22, a23, a31, a32, and a33 in the above equations are called conversion coefficients of color spaces and are generated on the basis of the laws of color matching, the color coordinates and the brightness of the display system, and the color coordinates defined in the specification. k1, k2, k3 in the above equations are coefficients of brightness ratio.
In the prior arts, the color coordinates of a display system are assumed to be constants. However, the color coordinates would change with different gray levels. Please refer to FIG. 1. FIG. 1 shows the relationship between the red color coordinates and the gray levels in a plasma display panel. As shown in FIG. 1, the color coordinates change with gray levels.
If a display system always adopts color coordinates corresponding to a high gray level to adjust the input images, the input image with low gray levels can never be displayed correctly. On the contrary, if a display system always adopts color coordinates corresponding to a low gray level to adjust the input images, the input image with high gray levels can never be displayed correctly.
Accordingly, one main purpose of this invention is to provide a method and an apparatus for adjusting an input image on the basis of the characteristics of a display system. Compared with the prior arts, the method and the apparatus according to this invention adjust the gray levels of an input image on the basis of the specification and the characteristics of the display system. That is to say, the method and the apparatus according to this invention can assist display systems to select proper gray levels for an input image such that the input image can be displayed correctly without color inaccuracy.